1. Field of the Invention
The present invention relates to a printer that performs printing by transferring ink of an ink ribbon onto a printing medium by using a thermal head.
2. Description of the Related Art
Thermal transfer printers in which printing is performed by transferring ink of an ink ribbon onto a printing medium by using a thermal head have been used as printers for printing on printing media such as labels attached to a mounting paper and band-shaped sheets for tag fabrication. In thermal transfer printers, the printing is performed by transferring ink of an ink ribbon onto a printing medium by heat generated by a heat-generating body of a thermal head, while intermittently conveying the printing medium and the ink ribbon in the same direction and at the same speed.
Accordingly, a thermal transfer printer is provided with a platen roller that conveys the printing medium and ink ribbon and also with a ribbon conveying mechanism that is composed of a ribbon feed reel, a ribbon conveying roller, and a ribbon take-up reel. However, if the platen roller and the ribbon conveying mechanism are driven with separate motors, the motors are difficult to control and the cost rises. Therefore, a configuration can be considered in which the drive power of one motor is transmitted to both the platen roller and the ribbon conveying mechanism by using a timing belt and gears.
In belt drive mechanisms in which a drive power of a drive pulley is transmitted to a driven pulley via a timing belt, an idle pulley for adjusting the tension of the timing belt is disposed between the drive pulley and driven pulley, and if a belt drive mechanism of a multistage system is used, the number of idle pulleys has to be equal to the number of timing belts. As a result, the number of parts is increased, a space is required for disposing the parts, and the belt drive mechanism is difficult to assembly. Furthermore, the tension of the timing belt has to be measured by using an adjustment tool such as a push gage in order to adjust and verify the tension of the timing belt.
As a pertinent technology, Japanese Patent Application Laid-open No. 2002-200809 (page 1, FIG. 1) discloses a printer having a timing belt that transmits a drive power from a drive source (pulse motor) to a platen roller and a conveying roller, and a first tension member (tension roller) and a second tension member (tension pulley) that apply tension to the timing belt, this printer comprising a rotary member that rotatably holds any one tension member. With such a structure an error in tension occurring when only one tension member (tension roller) is used to rotate two rollers by a drive power of one motor can be eliminated and uniform tension can be obtained along the entire circumference of the timing melt. However, a space is required to arrange the two tension members, and the printer is difficult to assembly.